(Advice Needed)(Straight Male) How do I confront my roommate?

First time posting on reddit! I'm a straight guy and I have been friends with my roommate ever since high school. This one night I had to wake up at 2AM to do homework and I walk into something a little unexpected. I caught him masturbating to gay porn in the study room at 2 AM. He had his headphones on and he did not catch me walking in on him. His friend group in high school always joked around with my roommate being gay quite a bit. I want to be a good friend and try to confront him about this incident. I want to let him know that it is okay to come out and be gay. Is there any way I could help him come out?